Hi Everybody Some final feedback on the tail wheel shimmy I have experienced: I have changed the tail wheel to a softer type wheel and the shimmy stopped immediately. Although the previous tail wheel was only on the aircraft for less than 10 hours of flying time, the aircraft stood in the hangar for almost a year without flying. This might also have been a cause for the shimmy. I am now in the process of manufacturing a dolly wheel for the Dimona to take the load off the tail wheel for extended periods on the ground.
Thanks to everybody for the valuable information and help with this problem. I certainly appreciate it Kind Regards Mathys Kuhn Training Captain T: 0825685614 C: 0825685614 F: 016 9330248 e: [email protected]<mailto:[email protected]> From: [email protected] [mailto:[email protected]] On Behalf Of Michael Stockhill Sent: 06 October 2015 03:19 AM To: [email protected] Subject: Re: [DOG mailing list] More on shimmy and tyres We used to have much luck in the past balancing wood props by adding another coat of paint or more to the light end of the prop. MLS On Mon, Oct 5, 2015 at 4:33 PM, wallace barnes <[email protected]<mailto:[email protected]>> wrote: Hi All Just putting in my little bit. To balance tail wheel and dynamic balance of prop go to a Tyre place and get a card of stick on weights as used on mag wheels there are a range of weights on each card. We have added 10 gms to our new prop and the results are amazing. cheers Wally On 5/10/2015 3:13 PM, Ian Mc Phee wrote: Rob Thanks for that. I would never have thought of balancing tailwheel. I use square Mc ready tyres 6pr 250x4 as am sick of the bunnings ones from China. I can say with PIK20E prop it really helps as with falke fixed pitch prop but even better do a dynamic balance on the prop. Ian Mc Phee 0428847642 Box 657 Byron Bay NSW 2481 AUSTRALIA On 5 Oct 2015 4:10 pm, "Rob Thompson" <[email protected]<mailto:[email protected]>> wrote: Don't forget that if your tail wheel is out of balance it will be much more prone to shimmy. A static balance can be acheived quite easily. A tiny bit of lead sheet flashing cut out to size and glued, screwed or doubled sided taped in place will solve the problem. Just support the well oiled shaft and see which side of the wheel rotates to the bottom. cheers Rob Rob Thompson 0429 493828<tel:0429%20493828> Please note that my new email address is [email protected]<mailto:[email protected]> ________________________________ From: [email protected]<mailto:[email protected]> To: [email protected]<mailto:[email protected]> Date: Mon, 5 Oct 2015 11:21:28 +1100 Subject: [DOG mailing list] Shimmy and tyres I have suspected for a while now that the square profile tail wheel tyres are less prone to shimmy than the round ones. Yesterday we changed to a round profile and for the first time in ages got a bit of shimmy on bitumen on the take off roll. Landed on grass but I will test the theory more sometime soon. Rob Rob Thompson 0429 493828<tel:0429%20493828> ________________________________ Date: Mon, 5 Oct 2015 11:09:19 +1100 From: [email protected]<mailto:[email protected]> To: [email protected]<mailto:[email protected]> Subject: Re: [DOG mailing list] H36 Tail wheels I found out my previous message didn't get through because of file size. Here it is again. Michael is on the right track. The vertical shaft on any castor wheel has to be exactly vertical. What happens with the Dimona h36 is that shaft gets bent slightly due to potholes etc. and from then on you have shimmy. The bend can be barely visible. The more the bend the more the excitement. I have had both the straight tailwheel and the damped one and the only difference is in height. I have seen a " repaired " one that was made stronger and that stuffed the C of G. The one with the damper bracket weighs 725 grams. A new part definitely fixes the problem. Regards, John. On 3 October 2015 at 00:08, Michael Stockhill <[email protected]<mailto:[email protected]>> wrote: I don't have the W&B info on my friend's H-36 here, but I do remember weighing it and finding the numbers way aft, somewhere on either side of the aft limits when flown solo. My own H-36 is fine. I can't account for the difference, suspecting perhaps an undocumented heavy repair, and the very lavish heavy beautiful refinish that was done. It has been a few years, but I did some calculations for adding a weight in the nose, but with the relatively short arm it was impractical. Life is great, MLS On Thu, Oct 1, 2015 at 8:19 PM, Nigel Baker <[email protected]<mailto:[email protected]>> wrote: I am surprised by your comment on them being tail heavy. I have weighed 4 different H36 aircraft and they all came in close to each other in C of G. See attached for my own aircraft. Cheers. Nige. From: Michael Stockhill<mailto:[email protected]> Sent: Friday, October 02, 2015 11:04 AM To: [email protected]<mailto:[email protected]> Subject: Re: [DOG mailing list] H36 Tail wheels My friend tried a later-model tailwheel fork with the rubber dampers on his H-36. I wasn't present, but recall that it is far heavier and put an already tail heavy bird way out of CG limits. There were other issues that prevented retrofit, if I remember correctly. MLS On Thu, Oct 1, 2015 at 4:56 PM, Rob Thompson <[email protected]<mailto:[email protected]>> wrote: The early H36 models had a straight un-damped tail wheel fork which, due the wheels being forward of the centre of gravity and the heavy tail weight can induce some quite nasty oscillations. As a result of this Hoffman later introduced a new tail wheel which has shock absorbing rubbers. This reduces dramatically the oscillations but is more prone to shimmy. If the tail wheel cables are too tight the steering becomes VERY responsive to the slightest pedal movement. If the cables are too loose you get shimmy. Takes a bit of experience to know when it is just right. Real pain when you have to take the tank out each time to get it right! Rob Thompson 0429 493828 Please note that my new email address is [email protected]<mailto:[email protected]> ________________________________ From: [email protected]<mailto:[email protected]> To: [email protected]<mailto:[email protected]> Date: Thu, 1 Oct 2015 21:09:03 +0200 Subject: Re: [DOG mailing list] Morning Glory Cloud Documentary Most interesting and helpful thanks Michael. My Dimona is also a bit of a beast on the ground compared to other taildragger aircraft I have flown. I will keep you pisted. Thanks for taking the time to write the detail. Regards. Thys Sent from my Samsung Galaxy smartphone. -------- Original message -------- From: Michael Stockhill <[email protected]<mailto:[email protected]>> Date: 01/10/2015 20:57 (GMT+02:00) To: [email protected]<mailto:[email protected]> Subject: Re: [DOG mailing list] Morning Glory Cloud Documentary Hi, Mathys, I own an H-36 and also maintain one belonging to a friend. Between the two of us, we have had some interesting tailwheel issues. My bird was the scariest tailwheel aircraft I had flown ( about 800 hours in various Super Cubs, Cessna 180's and 185's and DH Beavers, etc.). If you breathed on the rudder pedals during takeoff or landing when the tailwheel was on the ground, it would threaten to leave the runway, and on two or three occasions I suffered PIO (pilot-induced oscillations) that shook my teeth. What I finally discovered was a logbook reference to a tailwheel fork repair. The fork was rewelded at that time with absolutely no trailing rake. We rebuilt it with 7 degrees aft rake and that demon was tamed. It now actually reminds me of a normally operating aircraft. In the case of my friend's Dimona, most landings resulted in scary tailwheel shimmy--I thought it would take off the tailboom. He mitigated this at first by making wheel landings and holding the tail off as long as he could. On the couple times I experienced it, I braked as much and as soon as possible to get slowed down. We tried various tailwheel tire pressures and checked balance, etc.. It has been a while, so my recollection is a bit vague, but what I did discover by looking at the tailwheel fork while installed, the shoulder of the weldment where the vertical shaft enters the lower flanged spacer was not parallel with the face of that spacer. Upon disassembly we were able to discern some bending of the shaft at that point (the shoulder of the weldment and the tailwheel vertical shaft). We had a whiz of a machinist fabricate a new shaft and other parts of the tailwheel fork. I test flew it afterwards and it was a different airplane. Rudder cables were also replaced at a later date. Hope some of that is of help to you. Michael Stockhill Polson, Montana, USA On Wed, Sep 30, 2015 at 3:40 AM, Mathys Kuhn <[email protected]<mailto:[email protected]>> wrote: Hi Everybody I operate a mid 80’s model Hoffma Dimona in South Africa. Lately I started experiencing a significant tailwheel shimmy at low speed after landing on a tar runway. Has anybody ever experienced something similar? ANY ADVICE? Many Thanks Mathys Kuhn Training Captain T: 0825685614 C: 0825685614 F: 016 9330248 e: <mailto:[email protected]> [email protected]<mailto:[email protected]> From: [email protected]<mailto:[email protected]> [mailto:[email protected]<mailto:[email protected]>] On Behalf Of Ian Williams Sent: 23 September 2015 10:56 AM To: [email protected]<mailto:[email protected]> Subject: Re: [DOG mailing list] Morning Glory Cloud Documentary Apparently only able to be viewed in Australia. Sent from my iPhone On 23/09/2015, at 13:05, Rob Thompson <[email protected]<mailto:[email protected]>> wrote: G'day All, For those of you who missed it, the Morning Glory Cloud Documentary is on SBS "Catch Up" http://www.sbs.com.au/ondemand/video/521484355510/secrets-of-a-strange-cloud cheers Rob Rob Thompson 0429 493828 P Please consider the environment before printing this e-mail. ________________________________ Attention: Please note: This email and its content are subject to the disclaimer as displayed at the following link http://www.comair.co.za/disclaimer.html. Should you not have Web access, send an email to [email protected]<mailto:[email protected]> and a copy will be sent to you. ________________________________ --------------------------------------------------------------------- You are subscribed to the Dimona Owners Group mailing list. 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